1. Field of the Invention
The present invention relates to a moving magnet type linear motor or a moving coil type linear motor.
2. Description of the Related Art
A linear motor is comprised of an assembly of a coil and a magnet, one constituting a stator while the other constituting a moving body (movable body) which is driven linearly. Both the moving coil and moving magnet type linear motors are controlled substantially in the same way. However, to clarify the invention, the two types of the motors are explained respectively hereinafter.
An example of the moving coil type linear motor is disclosed in Japanese Patent Application Laying Open (KOKAI) No. 59-70178.
The moving coil type linear motor is composed of a movable body and a stator. The movable body comprises a yoke, a coil support attached to the bottom of the yoke, axles disposed at the four corners of the yoke, with wheels each being rotatably attached to each axle, and an armature comprising three coil wirings disposed on the lower surface of the coil support in a side by side arrangement continuously along the moving direction of the movable body. Each of the coil wirings is connected to a terminal (not shown) in a connector through a printed wiring pattern formed on the coil support. The connector is connected to a control circuit (not shown) of a CPU (Central Processing Unit).
On the other hand, the stator comprises a longitudinal base plate having a guide step (or groove) along each side thereof for guiding the wheels of the movable body, a stator yoke fixed along the longitudinal center line of the base plate, and a number of magnets disposed on the stator yoke. Each magnet has a strip shape having a longitudinal direction disposed in the lateral transverse direction of the base plate. The magnets are arranged so that the poles N and S are alternately disposed along the longitudinal direction of the base plate. The armature is disposed facing to the magnets through a predetermined gap formed therebetween.
A hall element for changing the magnetic field is arranged corresponding to each of the coil wirings disposed on the lower surface of the coil support. The hall element is connected to the control circuit of the CPU through a terminal of the connector.
For the operation of the above mentioned structure of a linear motor, a driving current is applied to the coil wirings through the connector from an outside drive circuit so that the movable body is linearly driven to move on the stator due to the magnetic effect generated between the armature and the magnets.
It is to be noted that each hall element detects the electric field generated from the magnet facing to the element. The detection signal is transmitted to the control circuit of the CPU so as to control the timing of changing the energizing the magnets. Therefore, it is possible to detect the position of the movable body without using a brush.
On the other hand, an example of the moving magnet type linear motor is also disclosed in Japanese Patent Application Laying Open (KOKAI) No. 59-70178.
A moving magnet type DC linear motor is composed of a moving body (movable body) and a stator. The moving body comprises a yoke having a U-shaped section, magnets attached to the lower surface of the yoke, and wheels rotatably attached to each of axles disposed at the four corners of the yoke. The magnets are arranged so that the poles N and S are alternately disposed along the longitudinal direction of the stator.
On the other hand, the stator comprises a longitudinal base plate having a guide step (or groove) on either side thereof for guiding the wheels, a stator yoke fixed on the base plate along the longitudinal center line thereof, a plurality of armatures continuously disposed on the yoke each armature being composed of a coil, and hall elements for changing the magnetic field each disposed on one side of each armature.
The coils formed on the stator face to the magnet of the moving body through a predetermined gap. Each coil along with the hall element is connected to a drive control circuit of a CPU.
To function the above-mentioned construction of the moving magnet type linear motor, a current is selectively applied to a coil so that the moving body is linearly moved on the stator due to the magnetic effect between the coil and the magnet.
It is to be noted that in accordance with the above-mentioned structure of the moving magnet type linear DC motor, each hall element detects the magnetic field generated from the magnet facing to the coil and the detection signal is transmitted from the hall element to the drive control circuit of the CPU so that it becomes possible to detect the position of the moving body without using a brush.
In accordance with the above-mentioned moving coil or moving magnet type linear DC motor, the current supply from the drive control circuit to each of the coils is controlled by the CPU in accordance with the program arranged in the CPU so as to desirably drive the moving body to move linearly.
However, the control signal from the CPU is sometimes disturbed by the noise from outside, which results in malfunction of the coils and makes the moving body uncontrollable. This causes that the moving body overruns the stator out of the base plate and damages the motor system.